F650 CS 2 - spark 2005 : 1508: Rear sensor fault, signal implausible.

[stardust_59]

Hi everyone,
perhaps you can enlighten me on ABS fault 1508 which seems to be a sensor fault or signal path fault to the ABS. 

Description:

On a 2005 F650 CS 2 spark the ABS light came on.

The first fault showed 12772: Rear sensor fault, resistive.

After removing the rear ABS sensor from the axle housing at the excenter it showed iron dust and what seemed brake dust.
The rear axle housing and eccentric were cleaned with isopropyl alcohol and compressed air.

Another sensor was installed.
After installing the replacement sensor

1508: Rear sensor fault, signal implausible.
was shown.

The sensor was checked before installation and showed 3.1 kOhm resistance.
The original sensor , thought to be defective also showed 3 kOhm resistance.

The position of the eccentric axle housing was left unchanged.

Observation:

After installing the replacement sensor, the bike was driven for a couple of meters.
The ABS light turned on again.
When applying the rear brake - the ABS would 'fall through'.
That is - first pressure builds up on the brake pedal and is then released.
The effect is the same as when bleeding the ABS - which was done a few days before.
It seems that the ABS valve opened for some odd reason.

Wheel bearings are ok - there is no play at the rear hollow axle.
No rough running or grinding noises that would indicate defective bearings.

Logs:


#2018-01-01 19:33:59
#GS-911 Android V1.2
#F650CS 2 spark
Controller name: BMS-C2
Part: 07689873
HW Version: A
Diag Idx: 5
Manufacturing Date: 2005-03-08
Program release: 180E
Date release:: 180EE606
Manufacturer:: Hella KG
=========================

#2018-01-03 21:13:31
#GS-911 Android V1.2
#F650CS 2 spark
Controller name: ABS-N
Part: 07661881
HW Version: 17
Coding Idx: 0
Diag Idx: 11
Manufacturing Date: 2004-03-31
Software version: 17
Manufacturer: Nippon
==========================

#2018-01-03 21:13:36
#GS-911 Android V1.2
#F650CS 2 spark
1508: Rear sensor fault, signal implausible.

Question:

Does anyone have a reference resistance for the ABS sensors ?
If the copper is intact there should be a well defined resistance for said coil which allows to check if the sensor is intact or defective.

After having read about the effects of metal dust on magnetic ABS sensors , observed on R1200 GS and similar models - cleaning of the axle bearing area was the first thing to be done.
Did not help though...

Does anyone have an idea what else might have to be taken into consideration for diagnosing the root cause of E 1508 ?

Thanks & regards
Jan

[WayneC]

The wheel sensors are Bosch DF11 active components not passive so they are not a component you take resistance measurements from, the measurements are meaningless. There is a thread on the forum which shows how to work with DF11 sensors using low cost DSO on an R1200, it is worth reading

The "implausible signal" error code indicates there is likely a wiring fault back to the dash, was the replacement sensor fitted a new sensor ?

[stardust_59]

WayneC,
thanks for the hint on the sensor type and DSO check. Good point.

I do have a signal generator and some HP digital and analog Osci available, if necessary.
Will look into that.

Dash - good point.
The owner fitted LED instead of incandescent bulbs assuming that 'it doesn't matter'.
I wasn't too sure about 'doesn't matter'...

Replacement sensor is a used one from a well known seller (BMW Salvage , motorcycle breaker).
Seller claims that it was of an operational vehicle.

My taking of the 'signal implausible' error was that the BMS and the ABS may have differing signal input.
As the rear sensor also provides the dash or BMS with rear wheel roation signal - I was a bit puzzled about where to go next..

Time to fire up the lab...



I'll report back with whatever may be relevant.

Jan

[WayneC]

I should have said ABS not Dash, on an ABS machine the rear wheel sensor goes to the ABS then the signal is extended to the Dash & back to BMS

You dont need a signal generator, all you need to do is spin the wheel and you should see around 1v on a multi meter set to AC range

The CRO can be hooked up to the sensor lead to display the pulses, having a 100 ohm resistor in series in the lead and the CRO across the resistor would be the best but search for the thread I referred to, the owner learned to use a DSO and prove a sensor all the the space of 24 hours

[stardust_59]

WayneC, thanks again for clarifying.

signal path:

rear wheel ==> ABS ==> Dash ==> BMS

Quite a few fault points in there.

Ok - I'll check the sensors first.
Next - all connections from ABS to Dash to BMS.
The ABS connector being to most interesting , I guess.
We'll see.
I have a nice todo list now.

Any keywords to find the thread with the DF11 measurements ?
I'm out of luck finding it.
But I guess doing the AC voltage measurement will be good enough for a start.

Jan

[Jughead]

Have a look at this thread:
http://forum.hexcode.co.za/forum/index.php/topic,96.msg470.html#msg470

[WayneC]

The thread I was referring to is  http://forum.hexcode.co.za/forum/index.php/topic,1506.0.html

[stardust_59]

@Jughead - thanks for the thread link - I had a look at that one already. Will be considered.

@WayneC - many thanks for the link.

As weekend approaches I will have some time to tinker.

Scanned the web for DF11 datasheets.
Next to nothing.
Automotive folks are pretty tight lipped about these components...

I still wonder how a voltage can be induced if there are two Hall elements exposed to a changing magnetic field. But that is more of an academic question right now.

I'll go through the procedure - just to see if anyone Sensor is shot - or the other fault options (signal path) come into play.

[WayneC]

The info for the DF10/11 sensors is mainly in the Bosch Racing division but if you do a search for Hella wheel speed sensors you should find the overall concept pdf for modern sensors, the bikes use the option for a metal pulse ring on the wheel where cars can have it all internal to the wheel hubs

There is also a Bosch Sensor catalogue with mechanical and electronic specs

In essence they consist of a low voltage control IC which has a sensor back end then a front end current switch facing the ABS/Dash to provide a precise square wave form signal of around 1 volt across a resistor in the ABS/Dash. A reasonable description from the Hella manual is below

Method of operation
The active sensor is a proximity sensor with integrated electronics supplied with a voltage defined by the ABS control unit. For the pulse wheel, a multipolar ring may be used and may be positioned in a sealing ring of the wheel bearing.

Magnets with alternating poles are installed in the sealing ring (Fig. 3). The magneto-resistors integrated in the sensor electronics detect a rotating magnetic field when the multipolar ring rotates. The electronics in the sensor convert the resulting sinoidal signal into a digital signal (Fig. 4). The signal is transmitted to the control unit in the form of a current signal using pulse width modulation.

The sensor is connected to the control unit via a two-wire electric cable. The sensor signal is transmitted via the power supply wire. The other wire is used as an earth for the sensor. In addition to magneto-resistor sensor elements, Hall sensors are also used today that permit wider air gaps and react to the smallest changes in the magnetic field.

If a steel pulse wheel is installed in the vehicle instead of a multipolar ring, then a magnet is additionally installed on the sensor element. When the pulse wheel rotates, the constant magnetic field in the sensor changes. Signal processing and the IC are the same as in the case of magneto-resistive sensors.

[stardust_59]

@All - thanks for the input.

I did some more research and found a BOSCH Instruction document for German vocational school / apprentice training which shows more than is available elsewhere.

The BOSCH Motorsport catalogue lists the sensors and some nice gadgets - but there is no data sheet or detailed functional description.

Given the wide distribution of the DF11 sensors and their aftermarket availability for many automotive brands (Renault, Dacia, Ford, BMW , Mercedes etc) I am puzzled that hardly no detail information is avalailable - other than possibly confidential OEM / Tier1 documentation.

At any rate:as the document is in German I have translated the document and will provide it here.
I assume that the information is not confidential as it is vocational school teaching material.

If there are any doubts about copyright violation , please let me know and the documentation will be removed.

If there is a need for the  German laguage version this can be supplied as well.

Taking the information about the sensor and putting it into context will also allow to get better insight into the signal processing / input circuitry of the ABS system.

The core information I took from this document is that we are not dealing with voltage related signallling but we have a current loop system which is much more EMI resilient.
Measurement and test methods are thus different from voltage level based systems.

I will look into this and see if I can develop a simple standalone test method for the DF11 sensor, if at all possible.

=============================

Active wheel speed sensors from BOSCH

Introduction

The wheel speed sensor (DS) was originally developed for use in anti-lock braking systems (ABS).
As the safety systems evolved, the wheel speed sensor has become increasingly important.
The future active generation DF 11 provides additional information which can not be provided by conventional inductive (passive) measuring principles.

The wheel speed information can now also be used by transmission- , engine- , navigation-  and suspension control systems.

picture 1: Sample DF11 Sensor



====
Mode of operation and measuring principle

A sensor is called active,
if supply voltage is necessary for its function.
The DF11 is an active speed sensor.
It must be connected to a voltage source for operation.
It provides a signal with constant speed independent of the speed and uses the Hall effect when detecting the speed signal.

See picture 2: signal conditioning curcuit and principle

Example for sensor without additional signals.
The speed sensor can detect the speed signal from ferromagnetic gears, stamping plates or wheels with applied multipoles.

When using gears or stamping plates, a working magnet is inserted behind the measuring element.
The application of this measuring principle allows a speed measurement (distance measurement) up to near v = 0 km / h.

This also covers the stricter vmin-conditions for navigation systems, roll-back barriers, parking systems, etc.


Signal processing

For the signal transmission, a two-wire current interface is used.
The sensor is supplied by the vehicle electrical system voltage.
Reverse polarity protection diode and backup capacitor are provided in the control unit.
The sensor will provide a current signal.

The low current is interpreted as a low signal.
== ILow = residual current consumption of the active element

The high current is interpreted as a high signal.

IHigh = ILow + Delta I;
Delta I = additional current through a path parallel to the active element

In the control unit, the current coming from the sensor at a measuring resistor RM is converted into a voltage signal.
The evaluation circuit detects from the magnitude of the voltage whether a high or low signal is present, see Figure 3.

Signal level

Signal current:

Low = 7mA +/- 20%
High = 14mA +/- 20%

Duty cycle

TV = t high / T period
0.3 <TV <0.7

***

In addition to the mechanical differences such as design and cable outlet axial, radial or integrated connector
there are two main variants, each with two sub-variants

DF11s / DF11sM

Data Protocol:
Square wave signal as speed signal
functionality:
Speed signal (DZ) - frequency signal to the wheel speed

***
Intelligent sensors DF11 (i) variant

DF11i / DF11iM
Data Protocol:
Square-wave signal with additional information, which is transmitted in the pulse width modulation (PWM) process.

The width of the rectangular pulse contains the additional information,
while the distance between a pulse and the next but one pulse represents the speed information.

Functionality:

Speed signal (DZ) - a frequency signal proportional to the wheel speed.
Standstill detection (STOP) - the vehicle is stationary for longer than about 1 second or
if the power supply is switched on, the speed sensor sends a standstill pulse about every second.
This pulse can be used to monitor the proper condition of the speed sensor at standstill.
Direction of rotation detection (DR) - indicates the direction of rotation (right / left) of the wheel relative to the sensor mounting position.
Air gap reserve (LR) - indicates whether the magnetic field strength change is below a value necessary for proper operation.

Mounting position detection (EL) - indicates whether the magnetic field strength change is sufficient to ensure operation with great certainty.
The mounting position signal bit is output only up to approx. 20km / h.

Pulse wheel:

For DF11i - magnetic multipole wheel.
For DF11iM - gears or stamping plates


Note:
The abbreviation M stands for built-in magnet and i means intelligent.
The DF11i consists of 2 DF11s plus additional evaluation electronics.

Output Description

DF11s / DF11sM
Speed sensor output signal with rotating pulse wheel.
The signal is a square wave signal with constant amplitude, and the frequency is proportional to the wheel speed, see picture.

picture 2: showing
symmetrical square wave signal T HI = T LO


DF 11i / DF11iM
Speed sensor output signal with rotating pulse wheel.
The signal is coded as PWM signal with different pulse legths which provide additional information.

picture 4: PWM signals , interpretation

1 sensor-oriented speed signal
2 signal clockwise rotation and installation position insufficient
==> Pre bit-LOW

3 signal anti-clockwise rotation and mounting position insufficient
4 signal clockwise rotation
5 signal anticlockwise
6 Signal air gap reserve too low

[stardust_59]

Next step w.r.t fault diagnosis will be the setup of  a test harness to access the connector between Rear wheel sensor and ABS.
It is mechanically next to impossible to hook up 'normal' test leads to the male connector of the sensor.
This connector seems to be proprietary BOSCH - it does not resemble any of the AMP product line connectors.

Thus - 22-28 AWG male & female crimp inserts well be used to access the pins / slots of both ends with accessible leads in between.
Parts are ordered.

This will allow to check the first part of the signal path.


The dashboard connector seems to be accessible from reverse side.

This leaves in situ access of ABS and BMS connections to be resolved.

I would be happy to receive any hints on how to access the further signal path with all components in place - with priority on the ABS ==> Dash path from ABS connector location.
A9190 / 24 ==> X9001 / 3 - cable yellow 0.5mm (sheet VIII ABS)

Not sure if the use of a LED for H9190 (ABS warning lamp) has an impact in the behavior.

Secondary path to A9500 / BMS can be checked 'dry' - by just puling connectors off and checking lead resistance from X9001 / 6  via X9409 to units A9500 (BMS) / 21 color Blue Yellow, 0.5mm . (See sheet VII of wiring diagram)
There are no active components in that path.

[WayneC]

The sensor is the DF11s & male/female pins from STD electronics 0.1" connectors can be used at the socket under the seat to connect a 100 ohm resistor for signal testing as per the thread I referred to, you wont need to do anything re the Dash/BMSC other than confirm continuity of the wiring between them

[stardust_59]

WayneC - thanks.
Did some measuements and can confirm.
Pins are really thin though - thinner than the usual breadboard headers..

Waiting for material to arrive for making a test harness for hooking up my scope.

Might need it more than once and I am not a fan of shaky conections when scoping...

[stardust_59]

The saga continues...

Meanwhile the rear sensor was replaced with a new one (OEM BMW part).
Measurements were made and the sensor shows signals to the ABS.

After replacement of the rear sensor the symptoms persists:
No speedomeeter readout, ABS failure / blinking lamp.

The lead from the ABS connector to the Speedometer / tachometer unit connector shows continuity,
as well as the lead from the BMS connector to its connector pin on the Speedo unit.

I checked the Speedo unit's input stage for the ABS rear signal and discovered that there is in fact an analogue input stage using a two or three stage transistor inverter.
Why this was not implemented using an OP amp is beyond me.

I will later supply pictures of my findings on the speedo PCB.

As the error persists after replacing the rear sensor  - I thought that the connection of the Sensor Input from ABS to the output pin for the BMS on the Speedo PCB might be defective.

I was lucky to get a working 2000 F650 / ABS Speedo unit which was used on the F650 CS - the symptom remains.


No speedomeeter readout, ABS failure / blinking lamp.

After a few meters (about 100 m) the ABS light goes on and indicates ABS error.

I will yet have to read out the error but I guess it will be the same as before.

1508: signal implausible.

The last thing that possibly remains to do is to re-check the leads and measure signals on the Speedo PCB input side - after the Speedo unit connector.

Is there any thing else that might have to be taken into consideration as fault cause ?

 

[WayneC]

I checked the Speedo unit's input stage for the ABS rear signal and discovered that there is in fact an analogue input stage using a two or three stage transistor inverter.
Why this was not implemented using an OP amp is beyond me.

The Dash input stage is designed to work with the raw sensor signal input on non ABS models and then the signal from the ABS on ABS models, the first transistor detects the 20ma current switch from the sensor, from there the signal goes to the processor and separately out to the BMSC